1. Field of the Invention
This invention relates to a biocompatible support material and, in particular, to the use of a biocompatible support material as a substrate for impregnation with living cells to enable cell growth and division. The invention further relates to a biocompatible support material capable of being formed into a variety of prosthetic devices prior to impregnation with living cells.
2. Related Art
Numerous tissue materials and constructions have been proposed for use as temporary or permanent grafts in tissue repair. Feagin, Jr., Ed., The Crucial Ligaments/Diagnosis and Treatment of Ligamentous Injuries About the Knee (Churchhill Livingstone, N.Y., 1988) describes a number of partially bioabsorbable materials which have been investigated for use as prostheses such as ligament grafts. In Chapter 33 of this publication (Rodkey, "Laboratory Studies of Biodegradable materials for Cruciate Ligament Reconstruction"), it is reported that while a 100 percent biodegradable ligament fabricated from polyglycolic acid (PGA) was found to be safe, strong, well-tolerated and provided stability for the repaired anterior cruciate ligament in dogs, its complete resorption within five weeks makes it unsuitable for use in prostheses intended for humans since a human ligament prosthesis must provide support over a much longer period of time. It is further reported that a study in dogs of the intraarticular use of a partially biodegradable ligament prosthesis possessing a DACRON (i.e., DuPont's polyethylene terephthalate (PET)) and PGA core and a separate outer sleeve woven from PGA and Dacron of a different percentage of composition gave disappointing results.
U.S. Pat. Nos. 4,792,336 and 4,942,875 describe a surgical device for repairing or augmenting connective tissue and comprising a plurality of fibers, in which the majority of the fibers are in a direction essentially parallel to the length of the device and can be either 100 percent bioabsorbable or can contain a nonabsorbable component. Additionally, sleeve yarns consisting completely of absorbable material wrap around these axial or warp yarns.
Biomedical Business International Report No. 7041 (Second Revision, May 1986), "Orthopaedic and Diagnostic Devices" pages 5--5 to 5-12, identifies a variety of materials which have been used in the fabrication of prosthetic ligaments including carbon fiber, expanded TEFLON (i.e., DuPont's polytetrafluoroethylene), a combination of silicone and PET, polypropylene, polyethylene, nickel-chromium alloy fibers individually enclosed in synthetic textile or natural silk, carbon material coated with gelatin, polyester combined with PET fibers, bovine tissues, and others.
Other disclosures of tissue repair devices, such as ligament and tendon repair devices, are provided, inter alia, in U.S. Pat. Nos. 3,805,300; 4,187,558; 4,301,551; 4,483,023; 4,584,722; 4,610,688; 4,668,233; 4,775,380; 4,788,979; and PCT Patent Publication No. WO 89/01320.
Chapter 33 (page 540) of the Feagin, Jr. publication referred to above identifies the characteristics of an ideal ligament prosthesis as follows:
(1) it must be durable with adequate strength to withstand the extreme forces placed upon it, yet compliant enough to allow for repetitive motion without failure or excessive creep elongation; PA1 (2) it must be tolerated by the host with no antigenic or carcinogenic reaction; PA1 (3) if partially or completely biodegradable, the size of the individual fibers and the construction pattern must be appropriate to support and allow eventual reconstitution of the repaired structure with ingrowth of fibrous tissue that matures to normal or near normal collagen; PA1 (4) it must tolerate sterilization and storage; and PA1 (5) it should be easily implanted using surgical and potentially arthroscopic techniques.
Other approaches to tissue repair have been proposed. These approaches include grafting tissue from a patient's own body to the site needing repair. This technique is hampered by the limited amount of tissue available for autografting coupled with the necessity of a major surgical procedure required for its harvesting.
A further technique for tissue repair includes the growth, in vitro, of cells from a patient's body or cell line. In this technique, described in U.S. Pat. Nos. 4,418,691, 4,458,678, 4,505,266, and 5,041,138, the disclosures of which are all expressly incorporated by reference herein, the selected cells are cultured on biocompatible support media in a nutrient-enriched environment. When sufficient cell density has been reached, the support material with the cultured cells is implanted at the site of needed tissue repair. This method is limited by the stringent requirements for the support material which must be strong enough to support the fragile tissue for implantation, yet porous enough to permit diffusion of nutrients and waste products necessary for cell growth. Currently employed support materials do not sufficiently fulfill these requirements, limiting the size of the tissue culture which may be achieved for implantation and/or the success rate for the implantation. Additionally, prior art support materials cannot be formed into prosthetic devices of sufficiently small size, e.g., tubular structures on the order of 2 millimeters in diameter, to enable the use of this technique to repair sites of damaged tissue of small dimensions.
Thus a need exists in the art for tissue repair device and method which incorporates both the strength and resiliency of synthetic biocompatible implants with the tissue compatibility of grafting and cell seeding. Such a device would enable tissue repair of large sites of tissue damage with enhanced healing rates and decreased scar tissue formation.